Biosorption-driven Chromium Removal by Bacillus pumilus Isolated from Natural Wastewater: Characterization and Surface Morphological Transformations

Release of heavy metal-containing, especially chromium (Cr), untreated industrial effluents into the water resources pose serious ecological and public health concerns. Thus, the present study is an attempt to isolate, identify and characterize a native Cr(III) resistant bacterium and explore the pathway underlying its possible bioremediation potentiality for chromium. Primary analysis of the wastewater samples collected from a heavy metal contaminated pond revealed presence of Cr (0.31 ppm) beyond the permissible limit. Following culture, a pure bacterial isolate (C4) was recovered. Morphological and biochemical characterization identified C4 as a Gram-positive, rod-shaped and non-lactose fermenting bacterium capable of utilizing citrate as the only source of carbon and exhibiting positive catalase, oxidase, urease, and methyl red reactions, indicating considerable metabolic versatility. Molecular characterization using partial 16S rRNA gene sequencing identified C4 as Bacillus pumilus (GenBank accession number: PQ061175.1). Growth kinetic assay revealed its variable chromium tolerance and strong adaptability. Findings of the scanning electron microscopic studies demonstrated the phenotypic adjustments of C4 under chromium stress. FTIR spectral investigation demonstrated that the hydroxyl, amino, carboxyl, carbonyl, proteinaceous, lipid, and polysaccharide functional groups collectively contribute to the biosorption and immobilization of Cr(III) by Bacillus pumilus. Finally, atomic absorption spectroscopy (AAS) study confirmed superior Cr bio-absorption capacity (~22% in 24 h) of Bacillus pumilus. Collectively, our findings for the first time elucidate the explicit cell-wall biosorption mechanisms that make B. pumilus an exceptional environmentally sustainable biocatalyst for the restoration of industrial wastewater and ecosystems contaminated with chromium.